1. Field of the invention
The present invention concerns belt and roller conveyor devices for flat objects enabling these objects to be processed or operated on as they are being transported.
2. Description of the prior art
These flat objects may be mail packets, for example. A conveyor device of the type indicated above is used to transfer them from an unstacking device, which delivers them one by one, to a plurality of tamper modules in a sorting station which routes and stacks them according to their destination. During this transfer from the unstacking device to the sorter modules a processing station upstream of the sorting station determines the destination of each successive packet.
An organisation of this kind is known as such. The processing station may involve an operator reading addresses and manually controlling the coding of successive packets, optionally with the printing of destination bar codes on the packets, for batches of packets which do not carry any such destination codes. It may serve to read destination codes automatically from packets in batches of packets carrying such codes. It may also involve reading of addresses by the operator and computer-controlled re-addressing of the packets according to input information generated by the operator after reading the address and corresponding re-addressing information stored in memory, optionally with printing of the new address and the bar code of the new destination.
The sorting station may be formed by a series of tamper modules mounted along the conveyor device, each module consisting of a paddle for holding back an evolving stack of packets on a base plane which is advantageously inclined, with an input switching device in the module.
These processing and sorting stations of the conveyor device require the packets to have at each station speeds compatible with the operation or operations that they carry out. For example, the operator reads the address from a packet which is halted at a reading position while destination bar codes are printed on the packets by an ink-jet printer as the packets move at a speed in the order of 0.4 m/s. In the sorting station, on the other hand, correct insertion and tamping of the packets in the tamper modules require that the packets arrive at a high speed, in the order of 3.5 m/s. The conveyor device therefore comprises a variety of individual belt and pulley conveyors each having its own respective speed and together defining a continuous path of movement for the packets.
To save space the conveyor device has a trajectory with curved portions between the processing stations, for folding it back on itself with rectilinear portions retained at the processing stations. In a mail coding and sorting machine the address reading and coding station(s) are placed before the operator, the sort in station is to the side and the trajectory of the conveyor device forms a double-bend transition between them.
In machines for coding and sorting mail and other machines for processing flat objects conveyed along processing stations conveyor devices with a folded trajectory are not always satisfactory. The curved portions of the trajectory must have large radii of curvature, as appropriate to the nature of the objects (for example their stiffness and whether they contain carbon paper), which is detrimental to the objective of a compact implementation. Depending on the processing carried out, any such folding back on itself of the conveyor trajectory, which involves turning round the objects, may be incompatible with or prejudicial to the processing to be carried out at any of the stations. In particular, such turning round of packets may result in jamming at a sorting station on insertion of the packets into the tamper modules by snagging of the packet entering its module on the address window of the top packet of the stack already made up there.
An object of the present invention is to avoid these disadvantages by making it possible to convey objects separately from each other with a high degree of reliability and without risk of damage to said objects, within a compact implementation.